1. Field of the Invention
The present invention relates to a silicon carbide semiconductor device with a temperature detecting element.
2. Description of the Background Art
A semiconductor element using silicon carbide (SiC) is considered as a promising element to function as a next-generation switching element capable of realizing a high breakdown voltage, low loss, and high resistance to heat. Such a semiconductor element is expected to be applied in a power semiconductor device such as an inverter. However, a semiconductor device formed by using silicon carbide (silicon carbide semiconductor device) has problems remaining unsolved.
As an example, it is known that a temperature detecting element for use in control of the operation of a protection circuit is provided in a semiconductor device. If this semiconductor device is a conventional semiconductor device formed by using silicon (silicon semiconductor device), a diode made of polysilicon (polysilicon diode) is often used as the temperature detecting element. The polysilicon diode is formed by ion implantation of impurities (dopants) into a polysilicon film. In order to form the polysilicon diode on the silicon semiconductor device, ion implantation for forming a semiconductor element in a silicon substrate, and ion implantation for forming the polysilicon diode, may be performed at the same time, thereby minimizing increase of the number of manufacturing steps.
Meanwhile, manufacture of a silicon carbide semiconductor device requires ion implantation for forming a semiconductor element, and subsequent thermal processing at a temperature of 1500° C. or higher. So, in order to form a polysilicon diode for temperature detection on the silicon carbide semiconductor device, ion implantation for forming the semiconductor element, and ion implantation for forming the polysilicon diode, should be performed separately. This involves considerable increase of the number of steps, compared to manufacture of a conventional silicon semiconductor device.
Japanese Patent Application Laid-Open No. 63-213370 (1988) discloses a semiconductor device of a structure where an insulating layer having heat conductivity is formed on the source electrode of a power transistor, and a thin-film resistive element made of platinum or polysilicon is formed as a temperature detecting resistor on the insulating layer.
As described above, providing a polysilicon diode functioning as a temperature detecting element in a silicon carbide semiconductor device increases the number of manufacturing steps, leading to increase of manufacturing costs. Additionally, a silicon carbide semiconductor device is expected to operate under a high temperature, whereas a polysilicon diode is hard to operate under a high temperature of 200° C. or higher. So, a polysilicon diode cannot be used in a silicon carbide semiconductor device supposed to operate under a temperature of 200° C. or higher.